ab = c a If the coefficients a,b and c are real then either α and β are real or α and β are complex conjugates

Size: px

Start display at page:

Download "ab = c a If the coefficients a,b and c are real then either α and β are real or α and β are complex conjugates"

Jayson Logan
5 years ago
Views:

1 Further Pure Summary Notes. Roots of Quadratic Equations For a quadratic equation ax + bx + c = 0 with roots α and β Sum of the roots Product of roots a + b = b a ab = c a If the coefficients a,b and c are real then either α and β are real or α and β are complex conjugates Once the value α + β and αβ have been found, new quadratic equations can be formed with roots : Roots α and β α 3 and β 3 a and b Sum of roots (a + b) ab Sum of roots (a + b) 3 3ab(a + b) Sum of roots a + b ab Product of roots (ab) Product of roots (ab) 3 Product of roots ab The new equation becomes x (sum of new roots)x + (product of new roots) = 0 The questions often ask for integer coefficients! Don t forget the = 0 Example The roots of the quadratic equation 3x + 4x = 0 are α and β. Determine a quadratic equation with integer coefficients which has roots a 3 b and ab 3 Step : a + b = 4 3 ab = 3 Step : Sum of new roots a 3 b + ab 3 = ab(a + b ) = ((a + b) 3 ab) = 3 = 7 æ ç 6 è 9 + ö 3 ø

2 Step 3 : Product of roots Step 4 : Form the new equation a 3 b ab 3 = a 4 b 4 = (ab) 4 = 8 x + x = 0 8x + 66x + = 0. Summation of Series These are given in the formula booklet REMEMBER : n å = n r = S 5r = 5 S r Always multiply brackets before attempting to evaluate summations of series Look carefully at the limits for the summation 0 å = å 0 - å 6 n å = å n - å n r =7 r = r = r =n+ r = r = Summation of ODD / EVEN numbers Example : Find the sum of the odd square numbers from to 49 Sum of odd square numbers = Sum of all square numbers Sum of even square numbers Sum of even square numbers = = ( ) 4 =4å r r = 49 Sum of odd numbers between and 49 is å r r å r = = æ ç è 6 = = 085 ö 4 æ ø è ç ö ø

3 3. Matrices ORDER a ù ë b ú û a ë c b ù d û ú x x Addition and Subtraction must have the same order a ë c b ù d û ú ± e ë g f ù h ú = a ± e û ë c ± g b ± f ù d ± h û ú Multiplication a ù 3 ë ú b û = ë 3a ù 3b û ú 3 ë 5 4 ù û ú ë 3 0 ù 0 ú = 3 x + 4 x 3 û ë 5 x + x 3 3 x x 0 ù 5 x 0 + x 0 ú = 5 û ë 30 ù 50 û ú NB : Order matters Do not assume that AB = BA Do not assume that A B = (A-B)(A+B) Identity Matrix I = 0 ù AI = IA = A ú ë 0 û 4. Transformations Make sure you know the exact trig ratios Angle θ sin θ cos θ tan θ ½ ½ Undefined To calculate the coordinates of a point after a transformation Multiply the Transformation Matrix by the coordinate Find the position of point (,) after a stretch of Scale factor 5 parallel to the x-axis 5 0 ë ù 0 ú û ë ù û ú = 0 ù ë ú û (0,)

4 To Identify a transformation from its matrix Consider the points (,0) and (0,) ë ù û ú (,0) ð (4,0) (0,) ð (0,) Stretch Scale factor 4 parallel to the x-axis and scale factor parallel to the y-axis Standard Transformations REFLECTIONS 0 ù 0 ù in the y-axis in the x-axis ú ú ë 0 û ë 0 û Reflection in y = x 0 ù Reflection in the line y= (tan θ)x ú ë 0 û ENLARGEMENT k ë 0 0 ù k û ú Scale factor k Centre (0,0) STRETCH cos q ë sin q If all elements have the same magnitude then look at θ = 45 (reflection in y = (tan.5)x ) as one of the transformations sin q ù cos q û ú In the formula booklet a 0 ù ë 0 b û ú Scale factor a parallel to the x-axis Scale factor b parallel to the y-axis In the formula booklet ROTATION cos q ë sin q sinq ù ú cosq û cos q sinq ù ë si n q co sq û ú Rotation through θ anti-clockwise about origin (0,0) Rotation through θ Clockwise about origin (0,0) If all elements have the same magnitude then a rotation through 45 is likely to be one of the transformations (usually the second) ORDER MATTERS!!!! make sure you multiply the matrices in the correct order A figure is transformed by M followed by M Multiply M M

5 5. Graphs of Rational Functions Linear numerator and linear denominator y = 4x 8 x + 3 horizontal asymptote vertical asymptote y = (x 3)(x 5) (x + )(x + ) distinct linear factors in the denominator quadratic numerator vertical asymptotes horizontal asymptote The curve will usually cross the horizontal asymptote distinct linear factors in the denominator linear numerator vertical asymptotes y = x 9 3x x + 6 horizontal asymptote horizontal asymptote is y = 0 y = (x 3)(x + 3) (x ) Quadratic numerator quadratic denominator with equal factors vertical asymptote horizontal asymptote y = x + x 3 x + x + 6 Quadratic numerator with no real roots for denominator (irreducible) The curve does not have a vertical asymptote Vertical Asymptotes Solve denominator = 0 to find x = a, x = b etc Horizontal Asymptotes multiply out any brackets look for highest power of x in the denominator and divide all terms by this as x goes to infinity majority of terms will disappear to leave either y = 0 or y = a To find stationary points k = x + x 3 rearrange to form a quadratic ax + b x x + c = 0 + x + 6 * b 4ac < 0 b 4ac = 0 b 4ac > 0 the line(s) y = k stationary point(s) the line(s) y = k do not intersect occur when y = k intersect the curve the curve subs into * to find x subs into * to find x coordinate coordinate

INEQUALITIES The questions are unlikely to lead to simple or single solutions such as x > 5 so Sketch the graph (often done already in a previous part of the question) Solve the inequality (x + )(x +

6 INEQUALITIES The questions are unlikely to lead to simple or single solutions such as x > 5 so Sketch the graph (often done already in a previous part of the question) Solve the inequality (x + )(x + 4) (x )(x ) The shaded area is where y < < So the solution is x < 0, < x <, x > 6. Conics and transformations You must learn the standard equations and the key features of each graph type Mark on relevant coordinates on any sketch graph Parabola Standard equations are given in the formula booklet but NOT graphs Ellipse x y a + y b = Hyperbola x a y b = = 4ax æ ç x ö è a ø + æ ç x ö è a ø Rectangular Hyperbola xy = c æ è ç y ö b ø = æ è ç y ö b ø = You may need to complete the square x 4x + y 6y = (x ) 4 + (y 3) 9 = (x ) + (y 3) =

7 Transformations Translation a ù Replace x with (x a) Circle radius centre (,.3) ú ë b û Replace y with (y - b) (x - ) + (y - 3) = Reflection in the line y = x Replace x with y and vice versa Stretch Parallel to the x-axis scale factor a Stretch Parallel to the y-axis scale factor b Replace x with a x Replace y with b y Describe a geometrical transformation that maps the curve y =8x onto the curve y =8x-6 x has been replaced by (x-) to give y ù = 8(x-) Translation ë 0 û ú 7. Complex Numbers real z = a + ib imaginary i = i = Addition and Subtraction ( + 3i) + (5 i) = 7 + i (add/subtract real part then imaginary part) Multiplication - multiply out the same way you would (x-)(x+4) ( 3i)(6 + i) = + 4i 8i 6i = 4i + 6 = 8 4i Complex Conjugate z* If z = a + ib then its complex conjugate is z* = a ib - always collect the real and imaginary parts before looking for the conjugate Solving Equations - if two complex numbers are equal, their real parts are equal and their imaginary parts are equal. Find z when 5z z* = 3 4i Let z = x + iy and so z*= x iy 5(x + iy) (x - iy) = 3 4i 3x + 7iy = 3 4i Equating real : 3x = 3 so x = Equating imaginary : 7y = -4 so y= - z = i

8 8. Calculus Differentiating from first principles Gradient of curve or tangent at x is f (x) = You may need to use the binomial expansion Differentiate from first principles to find the gradient of the curve y = x 4 at the point (,6) f(x) = 4 f( + h) = ( + h) 4 = 4 + 4( 3 h) + 6( h )+ 4(h 3 )+ h 4 = 6 + 3h + 4h + 8h 3 + h 4 f( + h) f() h = 6 + 3h + 4h + 8h 3 + h 4 6 h = 3 + 4h + 8h + h 3 As h approaches zero Gradient = 3 You may need to give the equation of the tangent/normal to the curve easy to do once you know the gradient and have the coordinates of the point Improper Integrals Improper if one or both of the limits is infinity Very important to include these statements the integrand is undefined at one of the limits or somewhere in between the limits Very important to include these statements

9 9. Trigonometry GENERAL SOLUTION don t just give one answer there should be an n somewhere!! SKETCH the graph of the basic Trig function before you start Check the question for Degrees or Radians MARK the first solution (from your calculator/knowledge) on your graph mark a few more to see the pattern Find the general solution before rearranging to get x or θ on it s own. Example Find the general solution, in radians, of the equation cos x=3sin x (- sin x) = 3sin x (Using cos x + sin x =) sin x + 3 sin x = 0 (sin x + )(sin x ) = 0 no solutions for sin x = - sinx = ½ General Solutions p 5p x = pn + p 6, x = pn + 5p p + p 6 p + 5p 6 You may need to use the fact that tan q = sin q to solve equations of the form cos q sin (x 0.) = cos (x 0.) 0. Numerical solution of equations Rearrange into the form f(x) = 0 To show the root lies within a given interval evaluate f(x) for the upper and lower interval bounds One should be positive and one negative change of sign indicates a root within the interval Interval Bisection - Determine the nature of f(lower) and f(upper) sketch the graph of the interval - Investigate f(midpoint)- positive or negative? - Continue investigating new midpoints until you have an interval to the degree of accuracy required Linear Interpolation - Determine the Value of f(lower) and f(upper) sketch the graph of the interval - Join the Lower and Upper points together with a straight line - - Mark p the approximate root - - Use similar triangles to calculate p (equal ratios)

10 Newton- Raphson Method - given in formula book as x n + = x n f (x n ) f ' (x n ) Given in formula book When working with Trig functions you probably need radians check carefully! value of new approximation value of previous approximation - you may be required to draw a diagram to illustrate your method tangent to the curve at x n Gradient of the tangent = f (x n ) f(xn f (x n ) = ) x n x n + NB : When the initial approximation is not close to f(x) the method may fail! DIFFERENTIAL EQUATIONS - looking to find y when dy/dx is given x n+ - EULER s FORMULA y n+ = y n + hf(x n ) - allows us to find an approximate value for y close to a given point x n Given in formula book dy = dx f(x) h = step size Example dy = e cos x, given that when y = 3 when x =, use the Euler Formula with step size dx 0. to find an approximation for y when x =.4 x = y = 3 h =0. f(x) = e cos θ y = (e cos ) = (approximate value of y when x =.) y 3 = (e cos. ) = 3.63 (approximate value of y when x =.4). Linear Laws - using straight line graphs to determine equations involving two variables - remember the equation of a straight line is y = mx + c where m is the gradient c is the point of interception with the y-axis - Logarithms needed when y = ax n or y = ab x Remember : Log ab = Log a + Log b Log a x = x Log a

- equations must be rearranged/substitutions made to a linear form y 3 =ax + b plot y 3 against x y 3 =ax 5 + bx ( x ) y 3 x = ax 3 + b plot y 3 x against x 3 y = ax n (taking logs) log y = log a + n

11 - equations must be rearranged/substitutions made to a linear form y 3 =ax + b plot y 3 against x y 3 =ax 5 + bx ( x ) y 3 x = ax 3 + b plot y 3 x against x 3 y = ax n (taking logs) log y = log a + n log x plot log y against log x y=ab x (taking logs) log y = log a + x log b plot log y against x if working in logs remember the inverse of log x is 0 x EXAMPLE It is thought that V and x are connected by the equation V = ax b The equation is reduced to linear from by taking logs Log V = Log a + b log x Using data given Log V is plotted against Log x The gradient b is. 50 = The intercept on the log V axis is.3 So Log a =.3 a =0.3 =9.95 The relationship between V and x is therefore V = 0x 3

Roots and Coefficients of a Quadratic Equation Summary

Roots and Coefficients of a Quadratic Equation Summary For a quadratic equation with roots α and β: Sum of roots = α + β = and Product of roots = αβ = Symmetrical functions of α and β include: x = and